Oil sand generally comprises water-wet sand grains held together by a matrix of viscous heavy oil or bitumen. Bitumen is a complex and viscous mixture of large or heavy hydrocarbon molecules which contain a significant amount of sulfur, nitrogen and oxygen. The extraction of bitumen from sand using hot water processes yields large volumes of tailings composed of fine silts, clays and residual bitumen which have to be contained in a tailings pond. Mineral fractions with a particle diameter less than 44 microns are referred to as “fines.” These fines are typically quartz and clay mineral suspensions, predominantly kaolinite and illite.
The fine tailings suspension is typically 85% water and 15% fine particles by volume. Dewatering of fine tailings occurs very slowly. When first discharged in the pond, the very low density material is referred to as thin fine tailings. After a few years when the fine tailings have reached a solids content of about 30-35%, they are sometimes referred to as mature fine tailings (MFT). Hereinafter, the more general term of fluid fine tailings (FFT) which encompasses the spectrum of tailings from discharge to final settled state. The fluid fine tailings behave as a fluid colloidal-like material. The fact that fluid fine tailings behave as a fluid and have very slow consolidation rates limits options to reclaim tailings ponds. A challenge facing the industry remains the removal of water from the fluid fine tailings to increase the solids content well beyond 35% and strengthen the deposits to the point that they can be reclaimed and no longer require containment.
Accordingly, there is a need for an improved method of dewatering tailings.